ipn: set RouteAll=true by default for new accounts on iOS and Android (#16110)

fixes tailscale/tailscale#16082

RouteAll should be true by default on iOS and Android.

Signed-off-by: Jonathan Nobels <jonathan@tailscale.com>
(cherry picked from commit 842df37803)

ipn/prefs.go

@@ -721,9 +721,10 @@ func (p *Prefs) ControlURLOrDefault() string {
 // of the platform it's running on.
 func (p *Prefs) DefaultRouteAll(goos string) bool {
 	switch goos {
-	case "windows":
+	case "windows", "android", "ios":
 		return true
 	case "darwin":
+		// Only true for macAppStore and macsys, false for darwin tailscaled.
 		return version.IsSandboxedMacOS()
 	default:
 		return false